1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a sheet of paper, such as a copy machine, a facsimile and a printer.
2. Description of Related Art
An image forming apparatus equipped with multiple functions, which is simultaneously provided with various functions such as a printer, a scanner, a copy machine and a facsimile, has been widely used in recent years. In such an image forming apparatus, an exposing portion provided at each color forms a latent image on a surface of the photosensitive drum corresponding the color based on image data and then, a developing portion develops the latent image by using toner contained in the developing portion. Respective toner images formed on the photosensitive drums of respective colors are transferred to a image-forming position of an intermediate transfer belt and then, by transferring the toner images formed on the intermediate transfer belt to a sheet of paper conveyed from a paper feed tray, a desired color image is formed on the sheet of paper.
By the way, in an electrophotographic image forming apparatus, a temperature rises within the apparatus by any heating elements used during an image forming process, any movable members, which move accompanying any friction heat, and/or the like. This rise in temperature may have an influence on the image forming process. For example, in the developing portion, a friction heat is subject to occurrence on a bearing portion of a mixing portion which mixes binary developing powder containing toner and carrier, a surface portion of a roller for forming the binary developing powder as a thin film and/or the like. This friction heat may cause the toner to be molten.
Similarly, the exposing portion scans a surface of the photosensitive drum using laser beam, by driving a polygon motor to rotate a polygon mirror rapidly, to form an electrostatic latent image on the surface of the photosensitive drum. Since the polygon motor rotates rapidly in this moment, a load of the polygon motor increases so that its temperature rises. As a result thereof, a temperature difference occurs in respective exposing paths. This temperature difference may cause the exposing position to be made different from the normal one, which degrades color reproduction.
Accordingly, the past image forming apparatus is provided with a cooling path for taking the air thereinto and/or a cooling member such as a cooling fan or the like, which prevent a temperature within the apparatus from rising. For example, a passage is provided near the developing portion and by taking the air into the apparatus via this passage, the developing portion is cooled. The exposing portion is provided with a special passage for cooling the polygon motor that is a heat source and the polygon motor is cooled by the air taken from the special passage into the apparatus.
For example, Japanese Patent Application Publication No. 2006-343607 discloses an image forming apparatus which is provided with a passage for cooled air flowing from a surrounding area of an image writing portion toward a surrounding area of a developing portion. Particularly, three intake fans are attached to a side surface of a main body of the apparatus and the air taken into the apparatus is sent to upper and lower portions of the polygon motor in the exposing apparatus through ducts. Further, intake fans are attached to a back surface of the main body of the apparatus and the is air taken into the apparatus is sent to an exposing apparatus and/or a developing apparatus through ducts.